Optical/radio local access network

ABSTRACT

A communication system includes a plurality of nodes and a plurality of point-to-point links that interconnect the plurality of nodes into a network. Each node includes an optical switch to controllably route a plurality of in-ports of the optical switch into a plurality of out-ports of the optical switch. Each point-to-point link includes a free space optical channel. A first free space optical channel couples to a first node through a receive path and through a transmit path. The receive path couples to a respective in-port of the optical switch of the first node, and the transmit path coupled to a respective out-port of the optical switch of the first node. In an alternative embodiment, a communication hub includes a plurality of neighborhood links, and a trunk coupled between the optical switch and a free space optical channel link to the network. A method of communicating in a network having plural links includes sensing the presence of a received signal failure resulting from at least one of rain and fog. The method further includes sending data in a free space optical channel of the first link when the received signal failure sensed is due to rain and sending the data in an RF channel of the first link when the received signal failure is due to fog.

CROSS-REFERENCE TO RELATED APPLICATIONS

This nonprovisional application is a continuation of and claims priorityto U.S. application Ser. No. 11/894,928, filed Aug. 22, 2007 now U.S.Pat. No. 7,565,081, which is a continuation of U.S. application Ser. No.11/215, 903, filed Aug. 31, 2005, now U.S. Pat. No. 7,274,877, which isa continuation of U.S. application Ser. No. 10/691,949, filed Oct. 23,2003, now U.S. Pat. No. 7,010,227, which is a continuation of U.S.application Ser. No. 09/641,083, entitled “OPTICAL/RADIO LOCAL ACCESSNETWORK,” filed on Aug. 17, 2007, now U.S. Pat. No. 6,788,898 issued onSep. 7, 2004, which claims the benefit of Provisional Application60/197,220, filed Apr. 14, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a local access network that links nodeswith a free space optical channel. In particular, the invention relatesto a network that brings telephony and data services to the home withouta need for wire or fiber to the home.

2. Description of Related Art

Free space optical transmission links are known and can providebroadband service potentially superior to that of radio wirelessservices. However, the free space optical transmission links aredegraded in adverse environment conditions. It has been a challenge tooffer continued service when high data rate optical links areunavailable.

SUMMARY OF THE INVENTION

Free space optical channels link together plural distributed switchingnodes into a network. A central controller commands these nodes over aknown radio telephone system to select alternative network routes to adestination that will bypass adverse environment conditions.

It is an object of the present invention to provide a network withbroadband performance even in the presence of adverse link conditionssuch as rain or fog. It is a further object of the present invention toprovide 911 services and critical low speed data services in thepresence of adverse link conditions.

These and other objects are achieved in a communication system thatincludes a plurality of nodes and a plurality of point-to-point linksthat interconnect the plurality of nodes into a network. Each nodeincludes an optical switch to controllably route a plurality of in-portsof the optical switch into a plurality of out-ports of the opticalswitch. Each point-to-point link includes a free space optical channel.A first free space optical channel couples to a first node through areceive path and a through a transmit path. The receive path couples toa respective in-port of the optical switch of the first node, and thetransmit path couples to a respective out-port of the optical switch ofthe first node.

These and other objects are achieved in an alternative embodiment of acommunication hub that includes a plurality of neighborhood links tocorresponding users, an optical switch coupled to the plurality ofneighborhood links, and a trunk coupled between the optical switch and afree space optical channel link to the network.

These and other objects are achieved in a method of communicating in anetwork having plural links that includes sensing the presence of areceived signal failure by monitoring channel losses in a first link,the received signal failure resulting from at least one of rain and fog.The method further includes sending data in a free space optical channelof the first link when the received signal failure is sensed due to rainand sending the data in an DF channel of the first link when thereceived signal failure is sensed due to fog.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be described in detail in the following descriptionof preferred embodiments with reference to the following figureswherein:

FIG. 1 is a schematic diagram of a broadband local access communicationsystem according to the invention;

FIG. 2 is a schematic diagram of a metro communication network of thesystem of FIG. 1 according to the present invention;

FIG. 3 is a schematic diagram of a portion of a node of the metrocommunication network according to the present invention;

FIG. 4 is a schematic of an outdoor unit (ODU) according to the presentinvention;

FIG. 5 is an alternative configuration to process an inbound optical WDMsignal on a multi-mode fiber into an optical WDM signal on a single-modefiber according to the present invention;

FIG. 6 is a schematic diagram of a local communication hub according tothe present invention; and

FIG. 7 is a schematic diagram of a demultiplexer for wavelength divisionmultiplex signals as used in the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In FIG. 1, access communication system 1 includes metro gridcommunication system 10 as a first-level system, direct customerspecific point-to-point links to customer sites 104 as a second-levelsystem, and pole-to-home links to customers homes 102 from aneighborhood pole 100 as a third-level system. Communication system 1serves metropolitan areas characterized by tall buildings to supportnodes of the system in metro grid 10, and it extends to the limits ofneighborhoods 2 or suburbs of the metropolitan area. Each link of metrogrid 10 preferably supports an optical signal or channel 3 (as shown inFIG. 2) and an RF signal or channel 36 (as shown in FIG. 2) that may beselectively enabled depending on weather conditions.

Within neighborhood 2, towers and/or poles 100 often serve to supportnodes in the local neighborhoods. Services for the neighborhoods arewavelength multiplexed together (for optical signals) and/or frequencymultiplexed together (for RF signals) and linked between neighborhoodpole 100 and metro grid 10.

Some sites, for example a business in either the metro area or theneighborhoods, may require a dedicated high-speed link. To serve thisneed, a customer-specific point-to-point ink is established to customersite 104. Such a point-to-point link typically carries a singlewavelength optical signal and/or a single frequency RF signal.

Area communication system 1 is advantageously linked to othercommunications systems. For example, another communication system 5might be linked via fiber link 6 to are communication system 1, andcommunication system 5 might be, for example, a SONET ring system.

In FIG. 2, communication system 10 includes a plurality of nodes,depicted as nodes 12, 14, 16 and 18, that are typically located on thetop of buildings, at windows in buildings or on the outside walls ofbuildings in metropolitan areas and on towers elsewhere. Each node iscoupled to a network control system that includes central controller 20,land lines 22 and one or more radio towers 24. Radio towers 24communicate with the nodes over wireless links 26. The control systemmay advantageously include a typical cellular telephone system,controller 20 (located at a convenient location) and cell phonetransceiver 46 at each node to direct the operation of communicationsystem 10.

The nodes are configured into a network by a plurality of point-to-pointlinks 30 of which link 32 is typical. Each link, as depicted by link 32,includes a bidirectional (e.g., duplex) free space optical channel 34.However, in any single link, there may be only a unidirectional channel.Furthermore, in an alternative embodiment of the invention as discussedbelow, one or more links, as depicted by link 32, further includes radiofrequency (RF) channel 36. RF channel 36 and free space optical channel34 complement each other. The RF channel propagates better than theoptical channel through fog and the optical channel propagates betterthan a millimeter wave RF channel through rain.

Each node includes at least one outdoor unit 40 (hereinafter ODU), andtypically a plurality of ODUs. For example, eight ODUs 40 are depictedin FIG. 2 on the top of a building at node 12. Each ODU is coupled toswitch circuit 42 through respective cables 44. Each ODU couples freespace optical signals received over link 30 into cable 44, andpropagates optical signals in a fiber in cable 44 as free space opticalsignals over link 30. In some embodiments of the invention, each ODUalso couples data from an RF path received over link 30 into cable 44and propagates data over an RF path from cable 44 over link 30.Typically, cable 44 includes two fibers to carry inbound and outboundoptical signals and, if the respective link includes an RF channel, theODU includes inbound and outbound RF cables (e.g., coax cables). Switchcircuit 42 is controlled by controller 20 through cell phone transceiver46.

The free space optical channel (hereinafter FSOC) can transmit superhigh bandwidths that no other wireless technology can offer. However,the FSOC availability is degraded when fog sets in, A best way toharness the bandwidth offered by the FSOC technology is to use it in an“as available basis” and to have radio channels for backup andredundancy when the optical channel is unavailable. The drawback with aradio channel as a backup or for redundancy is that a radio channelcannot support the bandwidth that can be carried over an FSOC. However,a radio channel can continue to offer services at a lower data rate.

FIG. 2 shows four nodes in a network connected to each other. Fog cell38 is shown in this figure to show that an FSOC can go out of service.Also shown are laser beams and their wavelengths connect the FSOC links.The radio frequency chosen for the backup link should have complementarycharacteristics or should be fade-free for the link under consideration.For example, the optical channel and the radio channel should not fadeat the same time. The spectrum chosen for the radio link is either a 38GHz radio or an ISM band spectrum (i.e., industrial, scientific andmedical band including 5 GHz, 2.4 GHz, 960 MHz, 400 MHz and 200 MHzbands). The 38 GHz radio (mm-wave) fades under rainy conditions and doesnot fade when there is fog. This is because the wavelength of themm-wave is of the order of the size of raindrops. The converse appliesto the optical beams, where the optical wavelength is of the order ofthe size of the water fog droplet. As a result, in fog the optical beamscatter, resulting in heavy attenuation to the optical beam. To transmitat mm-wave band, one needs to own a license for the frequency spectrum.An advantage of this is that no interference or jamming by other mm-waveusers should occur.

With the growth in RF IC designs, there are radios available in thelicense-free ISM band. A 5 GHz radio in the UNI band is a good candidatefor the redundant path since this offers good transmissioncharacteristics, line of sight link and uses 802.11 as a standard. Inaddition to this backup radio link, cellular phone transceiver 46 isshown at each node. This may be a standard mobile cell radio connectedto the FSOC controller 20 located at a network operation center orelsewhere. Controller 20 communicates with all the cellular radios tosend commands and receive status information from all the nodes.

In FIG. 3, a portion of node 50 include ODUs 52, 54 and 56, cell phonetransceiver 46, switch 60, optical-to-electrical interfaces 62, andcables 44. Each ODU includes a telescope 74, an RF unit 76 and aninput/output interface 45. Interface 45 enables the ODU to send outboundsignal traffic from outbound fiber 78 selectably to either telescope 74or RE unit 76. Interface 45 also enables the ODU to receive inboundsignal traffic on inbound fiber 79 selectably from either telescope 74or RE unit 76. The routing of interface 45 is controlled by signals fromtransceiver 46.

Telescope 74 of ODU 56 focuses inbound optical signal 34 into amulti-mode fiber, and the inbound signal is routed through interface 45to inbound single-mode fiber 79. Optical-to-electrical-to-opticalinterface 62 also includes driver-amplifier and laser source 68 toprovide an optical signal that is coupled through input single-modefiber 70 into switch 60. Local controller 58 under commands fromcellular phone transceiver 46 controls switch 60 to reflect the opticalsignal into output single-mode fiber 72. The optical signal passesthrough output single-mode fiber 72, through single-mode fiber 78through interface 45 into telescope 74 of ODU 52 to transmit free spaceoptical signal 34 outbound.

Add and/or drop multiplexers 84 from the building in which node 50 islocated are coupled through electrical bus 82 and bus controller 80 intoor from bus 66. Add and/or drop fiber optic lines 88 from the buildingin which node 50 is located are coupled through converter 86 (e.g.,having a fused biconic taper and detector on the optical receive sideand a laser on the transmit side) through electrical bus 82 and buscontroller 80 into or from bus 66.

In the event that fog blocks the optical channel of the link served byODU 52, transceiver 46 communicates with controller 20 which in turnsends commands via radio link 26 or equivalent land line links to localcontroller 58. Local controller 58 commands interface 45 so thatoptically converted inbound radio signal 36 is coupled from RF unit 76,through interface 45 into inbound fiber 79 of cable 44 in the place ofthe optical signal from telescope 74. In a variant, some or all of theODUs include gimbals (one or two axes) and servo controllers commandedby cell phone transceiver 46 to repoint the telescope and RF unit.

FIG. 3 is an exploded view of a node, and it shows three FSOC linktelescopes on which are mounted mm-wave or ISM hand radio. Also shown inthis figure is a cellular radio output connected to local controller 58which, in turn, controls a MEMs (or other optical) switch. The MEMsswitch provides the redirection (routing) of the optical beams, which iscontrolled by a local controller. The inputs to the local controller arefrom the cellular radio terminal, or the redundant radio link. There arethree links at each node: first is an optical link for high-speed datatransmission; second is a radio link for redundant lower speed data; andthird is a cellular radio link for command and control. The command andcontrol information on the cellular radio is preferably fed to the radiolink to provide redundancy to the control data at nodes in cases whencellular link is not available. Additional redundancy is obtained bysending the data on the radio to the optical link either by FDM(frequency), TDM (time) or WDM (wavelength) on the optical wavelength.

The only elements of the link that need be on the roof, at a window oron a side of a building are the outdoor units (ODUs), In FIG. 4, anoutdoor unit includes telescope 74, rotation gimbal 47, nod gimbal 48,servo controller (not shown), the radio unit 76 and input/outputinterface 45. The ODU interfaces with two optical connectors 78, 79 thatform cable 44 (see FIG. 3). The optical transmit signal is connected tothe ODU by single-mode fiber 78 coming from the laser transmitter whichis located in an indoor unit (IDU). The optical receive signal frominterface 45 is connected to the IDU by single-mode fiber 79. Interface45 includes fiber optic splitter 45-1 to split the signal from fiber 78into two optical signals carried on respective fibers to RF detector76-1 and telescope 74, respectively.

RE unit 76 includes optical detector 76-1 (e.g., a photodiode) and lasersource 76-2 (e.g., a laser diode or an LED). Optical detector 76-1converts an optical signal received from splitter 45-1 into anelectrical signal to modulate the RF unit. Laser source 76-2 modulatesan electrical signal received by RE unit 76 into an optical signal fortransmission over a fiber to optical detector 45-2. Interface 45 furtherincludes optical to electrical converters 45-2 and 45-3 (also calleddetectors, e.g., photodiodes). Optical detector 45-2 receives theoptical signal from laser source 76-2 (or RF unit 76), and opticaldetector 45-3 receives the optical signal from telescope 74. Telescope74 concentrates the received signal into a multi-mode fiber that iscoupled to optical detector 45-3. The electrical outputs from detector45-2 and 45-3 are provided to single-pole double-throw electrical switch45-4. Detectors 45-2 and 45-3 are also coupled to signal quality monitor45-5 that is in turn coupled to control electrical switch 45-4. Monitor45-5 determines through which channel (optical or RF) the strongestsignal is received, and then commands switch 45-4 to provide thestrongest signal to laser source 45-6. Laser source 45-6 converts theelectrical signal into an optical signal on single-mode fiber 79. In theIDU, as shown by FIG. 3, the optical receive signal from fiber 79 isconverted to an electrical signal on electrical bus 66 by opticaldetector 64 (i.e., photodiode) and then re-modulated as an opticalsignal by laser source 68 (e.g., laser diode) and propagated over asingle-mode fiber into MEMS switch 60. Interface 45 is controlled bytransceiver 46 to selected either RF or optical duplex operation.

As shown in FIG. 3, co-located to the IDU is an electrical add-dropmultiplexer (ADM) 84 and connection to a passive optical node (PON)network 88. The optical beam received from a distant link is availableat the output of the ODU, which is connected to the IDU by a multi-modefiber. This allows all the active optical elements to be insider thebuilding in a controlled environment for reliability and flexibility tooperate.

Optical links are made out of the ODU and IDU. The IDU has the lasertransmitters and optical receivers. The power output and wavelength isselected by the IDU. The output from the laser is fed to the MEMsoptical switch for routing. The routed output of the MEMs switch isconnected to the telescope in the ODU by a single-mode fiber. Theoptical receiver at the IDU is connected by a multi-mode fiber from theODU. The optical receiver converts the optical signal into electrical.This allows the optical beam received through the free space to beconverted to electrical by direct detection.

In FIG. 5, a variant circuit 140 as an alternative configurationincludes a multi-mode wavelength demultiplexer 142 coupled betweeninbound multi-mode fiber 79 and optical-to-electrical-to-opticalinterface 62. Demultiplexer 142 separates the inbound WDM signal onsingle-mode fiber 79 into plural signals dependent on wavelength. In thefigure, the inbound signal is separated by demultiplexer 142 into threeoptical signals, defined by wavelengths λ₁, λ₂, λ₃, and the three singlewavelength optical signals are provided on output multi-mode fibers 144,146 and 148. The three single wavelength optical signals are processedthrough optical-to-electrical-to-optical interface 62 and, from there,are provided on respective single-mode fibers 154, 156 and 158.

Optical-to-electrical-to-optical interface 62 processes signals asdiscussed with respect to FIG. 3. Optical detector 64 converts anoptical signal on inbound multi-mode fiber (e.g., 144) into anelectrical signal on electrical bus 66, and laser source 68 (e.g., alaser diode) converts the electrical signal on electrical bus 66 into anoptical signal on a single-mode fiber (e.g., 154). A function ofoptical-to-electrical-to-optical interface 62 is to convert an opticalsignal carried in a multi-mode fiber into an optical signal carried on asingle-mode fiber. A difference between single-mode and multi-modefibers is the fiber diameter. For wavelengths in the 1550 nanometerband, a fiber having a diameter of from 9 to 12 microns will onlysupport a single mode. However, if the diameter were larger (e.g., 60microns or more), multiple modes could propagate within the fiber. Anoptical signal received by a telescope can be focused into a multi-modefiber to achieve low coupling loss. Optical-to-electrical-to-opticalinterface 62 detects the optical signal from a multi-mode fiber (e.g.,144, 146 or 148) and reconstitutes the optical signal in a single-modefiber (e.g., 154, 156 or 158) at respective wavelengths λ₁, λ₂, λ₃.

In FIG. 5, biconic taper fiber 152 (or similar functioning device)combines signals that are carried in single-mode fiber 154, 156 and 158and provides the combined WDM signal to optional optical amplifier 150.Amplifier 150 is preferably an erbium doped fiber amplifier (EDFA) butmay be of other design. Amplifier 150 provides the amplified signallevel that is provided to MEMS switch 60 (see FIG. 3).

Radio links of the system use LAN (10base-t or 100base-t) interfacecards. The data field in the LAN has the address and status informationof all the nodes in the network. This would allow any node in thenetwork to know the status of any other node. By providing a dedicateddata field in the LAN, it is possible to offer 911 services and a fewvoice calls. The rest of the data field is used for informationtransfer. When more than one branch fails, the “information data field”is shared by the failed branches as in the case of a LAN.

The purpose of the cellular link is to provide an interface to theremote controller to monitor and control the nodes. There is a cellularradio installed at each node that works with the local cellular radioprovider. When the optical received signal strength falls below acertain level, it generates an alarm that the cellular radio transmitsto the controller. The controller uses this information to send therequired commands to the nodes for reconfiguration. The cellular radiohas a data interface card to transmit locally generated alarms andstatus conditions and to receive commands from the remote controller.

The ADM and distribution cards are located at the IDU. The electricalsignals generated by the optical receiver are used locally fordistribution or regenerated if required and sent to a laser for routingthrough the links, or to a PON for distribution. The E bus shown in FIG.3 has all the electrical signals obtained from the optical receivers.

In a second embodiment, this architecture has only two layers, opticaland cellular without the radio layer. This would allow for costreduction and spectrum unavailability for the radio link. In thisarchitecture, the optical link provides the data throughput, and thecellular radio provides the monitoring, management of the network nodeand a 911 call capability.

As discussed with respect to FIG. 1, a customer specific point-to-pointlink to customer site 104, for example a business, is typical of a sitethat may require a dedicated high speed link in either the metro area orthe neighborhoods. To serve this need, a point-to-point link isestablished that typically carries a single wavelength optical signaland/or a single frequency RF signal (e.g., a 38 GHz radio). The opticaland RF channels each serve as a back up link for the other based onweather where multiple broadband radio links are required at the subjectnode location. Cellular or other low data rate wireless links are usedfor monitoring, command and control.

In FIG. 6, local hub 100 is mounted on a neighborhood pole or suitabletall structure in the neighborhood to be served with “to the home”service. Local hub 100 includes optical-to-electrical-to-opticalinterface 62, electro-optical switch 60, and cellular phone transceiver46. The cellular phone transceiver controls the local hub by relayingcommands received from radio tower 24 over wireless link 26 andreporting status to radio tower 24 over wireless link 26. Control oflocal hub 100 by way of the radio link is the same as control of thenetwork depicted in FIG. 2.

Local hub 100 includes a WDM or DWDM fiber coupler 120. Coupler 120 is atree configuration providing for the multiplex and/or demultiplex ofmultiple wavelength optical signals in a fiber. FIG. 7 shows a 1×16fiber-based coupler 120 where a single fiber carrying 16 wavelengths (λ₁through λ₁₆) is demultiplexed into 16 individual fibers, each carrying acorresponding wavelength.

Local hub 100 further includes 1×2 electro-optical switch 116. Hub 100is connected through 1×2 electro-optical switch 116 to the networkdepicted in FIG. 2 over fiber links 114 or over free space opticalchannel (HOC) link 112. A wavelength division multiplexed (WDM) opticalsignal received from a network is demultiplexed in coupler 120 androuted appropriately through switch 60 and interface 62. A demultiplexedoptical signal of the appropriate wavelength may be routed to homes 102over a distance of several hundreds of meters using FSOC telescopesmounted on the pole, tower or building on which the hub is mounted. Whenhome 104 is too far from hub 100, a length of optical fiber may be usedto carry the signal to an FSOC telescope located closer to the home.When plurality homes 105 are too far from hub 100, a length of opticalfiber is used to carry optical signals to an all-fiber-based opticalcoupler 106, suitably located to broadcast via FSOC telescopes to homes105. Similarly, all-fiber-based optical coupler 106 separates otherwavelengths and can deliver data on fiber cables 108 directly to one ormore homes 107 without going through FSOC telescopes. In exactly thereverse direction, optical signals from homes 102, 104, 105 and 107 aretransported to interface 62 and switch 60 and then to coupler 120.Coupler 120 is coupled through switch 116 either to FSOC link 112 to thenetwork of FIG. 2 or to optical fiber cables 114 to the network of FIG.2.

Routing of the data network through the FSOC link is shown in FIG. 6. Inthis embodiment the optical and radio architecture is used for low costwide distribution local access “pole to home”. In this arrangement amicro local hub is located at the base of a suitable structure (pole,tower or building), or similarly to the above embodiments, roof mounted.The local hub is designed to receive fiber fed optical signals that maybe from a FSOC link or from fiber routed to the neighborhood. Opticalsignals entering the optical-to-electrical-to-optical transceiverinterface will be in a single-mode format where possible, but in thecase of the FSOC receiver interface, will be a multi-mode format untilsuch time as a low loss multi-mode to single-mode conversion can beachieved.

The fiber and/or FSOC interface is routed through a 1×2optical/electrical switch. Note that the multi-mode signal from the FSOCdevice is first electrically detected and converted back into asingle-mode optical signal prior to going through the optical switch.

The optical signals are then fed to all-fiber based couplers with a treestructure providing the multiplex of multiple wavelengths in a 1×2, 1×16or 1×N configuration (providing customer wavelength selected allocation,see FIG. 7). Such devices allow customer data to be loaded onto a singlewavelength. Standard wavelength non-specific all-fiber technology can beused in this application, but at the cost of significantly lowering theoptical signal to noise ratio and a requirement that detectors at thecustomer end must receive and process all the transmitted wavelengths.

The wavelength selected individual fiber outputs are then directed tothe network side of a MEMS-based or other optical switch, each with a1×16 to 1×N selectable output. The presence of the switch is similar tothe above-described MEMS switch embodiment in that it provides anoverlaying RF cellular-based switch selection architecture for routingand restoration of customer channels; it also provides an addedcapability of service activation/deactivation via remote (cellularcontrol of the switches' micro optical mirrors).

The single-mode specific wavelength optical signal output to thecustomer is fiber-fed to a dedicated ground-level local“fiber-to-the-home” or a low cost FSOC device mounted on a suitablestructure for short 100-200 meter transmissions to the customer premise.A number of optical, radio, fiber and cable “deployments to the home”scenarios are possible with this MEMS-based optical/RF hub application.

The return path is a single-mode signal for fiber-dedicatedarrangements; but a multi-mode signal received from the FSOC bulk opticsfocal plane is electrically detected and converted back to a single-modeoptical signal via a low cost single wavelength laser transmitter andlaunched back into the MEMs switch for return path routing. A moreflexible embodiment would use wavelength selectable lasers for thereturn path located at the hub's customer-sideoptical-to-electrical-to-optical interface where by selection ofsuitable single-mode wavelengths that can be multiplexed back into thenetwork fiber.

The MEMs switch channels the return path optical signal to a suitablereceiver port on the network all-fiber couplers side of the MEMs switch.The all-fiber couplers multiplex the multiple single-mode wavelengthreturn path signals, regenerate them if necessary, or launch them backinto the neighborhood's return path fiber or roof-top FSOC device.

Having described preferred embodiments of a novel local access network(which are intended to be illustrative and not limiting), it is notedthat modifications and variations can be made by persons skilled in theart in light of the above teachings. It is therefore to be understoodthat changes may be made in the particular embodiments of the inventiondisclosed which are within the scope and spirit of the invention asdefined by the appended claims.

Having thus described the invention with the details and particularlyrequired by the patent laws, what is claimed and desired protected byLetters Patent is set forth in the appended claims.

What is claimed is:
 1. A communication system comprising: a plurality ofnodes, each node including a switch to controllably route signals from aplurality of in-ports of the switch into a plurality of out-ports of theswitch; a plurality of point-to-point links that interconnect theplurality of nodes into a network, each point-to-point link including afirst channel for coupling to a first node through a receive path and asecond channel for coupling to a second node through a transmit path;and a wireless network controller coupled to each one of the pluralityof nodes over a radio telephone system, the wireless network controllerfor monitoring the plurality of nodes and providing control signals toaffected nodes to re-route signals through other nodes in a presence ofadverse link conditions along any one of the plurality of point-to-pointlinks.
 2. A communication system as defined in claim 1 wherein there-routed signals include 911 services signals.
 3. A communicationsystem as defined in claim 1 wherein the re-routed signals includes lowspeed data signals.
 4. A communication system as defined in claim 1wherein the wireless network controller is configured to monitor channellosses indicating that the adverse link conditions are associated withadverse weather conditions.
 5. A communication system as defined inclaim 1 wherein the radio telephone system comprises a cellular radio.6. A communication system as defined in claim 1 wherein at least aportion of the point-to-point links comprise a free space opticalchannel, and wherein an optical received signal strength of the freespace optical channel falling below a certain level is indicative ofadverse link conditions.
 7. A communication system as defined in claim 6wherein each node comprises an optical receiver configured to generatean alarm responsive to the optical received signal strength fallingbelow a threshold level.
 8. A communication system as defined in claim 6wherein at least a portion of the point-to-point links further comprisea radio frequency channel.
 9. A method comprising: monitoring, by awireless network controller, a plurality of network nodes, at least someof the plurality of network nodes being in communication with others ofthe plurality of network nodes through respective point-to-point links,each point-to-point link comprising a respective free space opticalchannel; detecting an optical received signal strength of a free spaceoptical channel of the respective free space optical channels fallingbelow a certain level; providing, by the wireless network controller,control signals to reconfigure the plurality of network nodes; andre-routing signals along one of the respective point-to-point linksthrough other network nodes responsive to detecting the optical receivedsignal strength falling below the certain level.
 10. The method of claim9, wherein the monitoring comprises coupling the wireless networkcontroller to each network node of the plurality of network nodes over aradio telephone system.
 11. The method of claim 9, wherein each networknode of the plurality of network nodes controllably routes signals froma plurality of in-ports of a switch into a plurality of out-ports of theswitch.
 12. The method of claim 9, wherein each respectivepoint-to-point link includes a first channel for coupling to a firstnetwork node of the plurality of network nodes through a receive pathand a second channel for coupling to a second network node of theplurality of network nodes through a transmit path.
 13. The method ofclaim 9, wherein monitoring, by the wireless network controller,comprises detecting an alarm.
 14. The method of claim 9, whereindetecting an optical received signal strength of the respective freespace optical channel falling below a certain level is indicative ofadverse link conditions along the respective point-to-point link.
 15. Amethod comprising: detecting, within a wireless network, an opticalreceived signal strength of a free space optical channel of a networkroute to a destination, falling below a threshold level, wherein thenetwork route comprises a first group of nodes of a plurality of nodesof the wireless network; selecting, responsive to detecting the opticalreceived signal strength falling below the threshold level, analternative network route to the destination comprising a second groupof nodes of the plurality of nodes of the wireless network; andcommanding, by a central controller in radio telephone communicationwith the plurality of nodes of the wireless network, a reconfigurationof the plurality of nodes of the wireless network according to thealternative network route.
 16. The method of claim 15, wherein theoptical received signal strength falling below the threshold levelresults from adverse environmental condition, and wherein the selectingof an alternative network route to the destination comprises bypassingthe adverse environmental condition.
 17. The method of claim 15, whereinthe central controller is in cellular radio telephone communication withthe plurality of nodes of the wireless network.
 18. The method of claim15, further comprising: generating an alarm responsive to the opticalreceived signal strength falling below the threshold level; andtransmitting the alarm to the central controller by way of radiotelephone communication.
 19. The method of claim 15, commanding thereconfiguration of the plurality of nodes comprises sending commandsfrom the central controller by way of radio telephone communication.